A month ago, I was staging the Interop Labs, with a particular personal focus on VoIP on 802.11. At that point, I promised to investigate what improvement Wi-Fi Multimedia (WMM) prioritization makes to voice quality. The Interop show floor is a terrible radio environment. From the Interop Labs booth, I can see between 40 and 70 access points. In this environment, WMM makes a huge difference.
We’re running the Interop Labs on Asterisk. To show off the difference in voice quality, I configured Asterisk to record the incoming voice stream from the 802.11 phone. You can listen to the results, and see what a difference WMM makes. Both recordings were made just after lunch (about 1:20 pm) on the second day of the show, which was one of the busiest times for us in the booth.
So, without further ado, here are the three recordings:
- Introductory remarks. Before the show opened, I recorded a 5-minute introduction to the technology and the challenges we hoped to investigate. This recording was made from a wired phone about ten minutes before the expo floor opened.
- Non-prioritized voice. This recording is a bit over one minute long, and was made between a phone and an access point that don’t support WMM. You can hear the effects of the heavy background traffic in the frequent dropouts.
- WMM-prioritized voice. In the final 2-minute long recording, the voice is prioritized with WMM between the Unex WP2 phone and Trapeze wireless infrastructure. (This is one of the first, if not the first, public interoperable WMM demonstration.) Although the conversation breaks up, it happens less frequently and the dropouts are far less severe.
One important note: I recorded these samples at the PBX, so there’s only one wireless hop in them. A call between two wireless phones would have double the opportunity for packet loss or delay, and the difference between prioritized an unprioritized traffic would be even more striking.